Well (sticking to my guns here :-) ) given a choice of putting the singles into a precisely correct directory and having directory fragmentation OR using the primary artist and keeping the directories simple, I would personally choose the latter. However I accept that this is a personal view and that many others would prefer correct naming.

So I propose to keep the %_primaryartist% variable so that people can use this if they wish, and to switch back to use of %artist% in the renaming string.